How to supress bpy render messages in terminal output?
The following output redirection proposed here does work:

# redirect output to log file
logfile = 'blender_render.log'
open(logfile, 'a').close()
old = os.dup(1)
sys.stdout.flush()
os.close(1)
os.open(logfile, os.O_WRONLY)

# do the rendering
bpy.ops.render.render(write_still=True)

# disable output redirection
os.close(1)
os.dup(old)
os.close(old)